Those black borders at the top and bottom of the screen.

[ChrisW6ATV]

Originally Posted by merrylander

Even with HDTV you will still get this letterbox effect with some movies on DVD because Hollywood's widescreen and NTSC's widescreen do not always agree.

The aspect ratio chosen for HDTV, also used in other countries for standard-def and on widescreen DVDs, is 1.77:1 or 16:9. This ratio is basically an average of all the other ratios used over the years for TV and movies. Movie directors choose different screen ratios for different types of movies, typically wider 2.35:1 or 2.4:1 for action and dramas, and 1.85:1 for most comedies as well as many other films.

Attempting to "fill up the whole TV screen with content all the time" by chopping the sides of wider movies or exposing content from movie negatives that was not used in theaters makes no more sense than going to an art gallery and modifying the paintings so they all fit in a 16x20-inch frame.